The present invention relates to methods for biologically treating wastewater, groundwater and soil washwater contaminated with ammonium perchlorate based rocket propellants, and specifically to an economical and environmentally safe method for treatment and disposal of process wastewater containing explosive materials such as may be generated from the manufacture, maintenance, refurbishment and disposition of solid propellant rocket motors and the remediation of groundwater or soil washwater contaminated with perchlorate based material.
Existing methods for disposal of ammonium perchlorate based solid rocket propellants consist generally of open burning/open detonation of the fuel or of static firing of the fueled rocket motor. Disposal by open burning or detonation is performed in an open pit where the propellant burns in an uncontrolled manner and may explode and spread in the area immediately surrounding the burn site. This exploded material serves as a contamination point for soil and groundwater. Static firing of a rocket motor produces the same concentration of exhaust gases as are produced during a normal launch. In either disposal procedure, hydrogen chloride gas is produced at a rate of about 0.2 pound per pound of burned propellant, and nitrogen oxides and various hydrocarbons are also produced. Open burning or detonation of the propellant or static firing of the fueled rocket may therefore be considered environmentally unacceptable.
The invention solves or substantially reduces in critical importance problems in the related prior art by providing a two stage anaerobic-aerobic process for the biological reduction of wastewater containing ammonium perchlorate which may be generated from the manufacture, maintenance, refurbishment and disposition of Class 1.1 and 1.3 rocket motors or the remediation of soils an groundwaters contaminated with said materials. Class 1.1 rocket motor propellants typically contain 14% ammonium perchlorate, 14% HMX and 30% nitroglycerine as oxidizers, 20% aluminum fuel and 22% nitrocellulose binder. Class 1.3 propellants typically contain 70% ammonium perchlorate oxidizer, 17% aluminum fuel and 13% PBAN binder. Wastewater is generated from rocket motor washout operations in which propellant is removed from the motor casing with high pressure water. For class 1.3 propellants, about 7550 gallons of liquid containing about 10% by weight of ammonium perchlorate normally are produced per 10,000 pounds of propellant. Wastewater treatment according to the invention comprises reducing perchlorate to chloride in a first stage anaerobic reactor using a specific unique microorganism in a mixed culture under controlled pH and temperature conditions, followed by reduction in a second stage aerobic reactor of the organics produced in the anaerobic reactor. The effluent liquid may be disposed of routinely to a conventional sanitary sewer system.
Known in the art is a method for biochemical reduction of chromium or chlorine inorganic oxygen containing compounds in industrial wastewaters (U.S. Pat. No. 3,755,156). The process involves the mixing of said wastewaters with municipal sewage whose biological oxygen demand (BOD) exceeds the amount of oxygen in the inorganic chromium and chlorine oxides. The combined wastewaters, municipal sewage and recycled acclimated sludge are maintained under anaerobic conditions with the bioreduction of perchlorates occurring at volumetric rates of approximately 12 mg ClO.sub.4.sup.- /hr per liter. The treated wastewater is then passed to an aeration chamber for the further reduction of BOD.
Also known in the art is the controlled addition of the micro-organism Vibrio dechloraticans Cuznesove B-1168 to a similar mixture of perchlorate or chlorate bearing industrial wastewater and municipal sewage with bioreduction of those compounds to chloride salts (U.S. Pat. No. 3,943,055). This process increases the volumetric bioreduction rate of perchlorate to over 100 mg/hr per liter compared to the previous method and improves the specific perchlorate degradation rate to 70 mg ClO.sub.4.sup.- /hr per gram of biomass solids.
The invention has advantages over the prior art in that, (1) it can reduce perchlorate wastewater concentrations as high as 7750 mg per liter, a 26 fold increase over previous methods; (2) the organism used (HAP1) has a specific degradation rate of at least 1492 mg ClO.sub.4.sup.- /hr per gram of dry biomass, a 21-fold increase over previous methods; (3) it has a demonstrated continuous volumetric degradation rate at least two-fold higher (221 mg ClO.sub.4.sup.- /hr liter) than previous methods at ten-fold higher perchlorate concentrations (3000 mg/liter); (4) it provides a self-contained optimum nutrient feed system and thus does not require a municipal sewage source for operation. This is a requirement for the operation of this type of system in remote demilitarization processes and contaminated soil and groundwater sites.
It is a principal object of the present invention to provide a method for treating and disposing of wastewater containing perchlorate-based explosive materials.
It is another object of the invention to provide an economical and environmentally safe process for the biotreatment of perchlorate wherever desired, including, but not limited to, rocket motor washout systems, contaminated demilitarization facilities, contaminated soils or contaminated groundwater.
A further object of the invention is to provide a unique microorganism capable of degrading perchlorate at rates and concentrations significantly higher than reported in the prior art.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.